1. Field of the Invention
This invention relates generally to optimizing the tradeoff between efficiency and linearity in a radio frequency (RF) power amplifier in a wireless communication device transmitter, and, more particularly, to a power amplifier including a desensitized bias circuit.
2. Related Art
With the increasing availability of efficient, low cost electronic modules, mobile communication systems are becoming more and more widespread. For example, there are many variations of communication schemes in which various frequencies, transmission schemes, modulator techniques and communication protocols are used to provide two-way voice and data communications in a handheld telephone-like communication handset. While the different modulation and transmission schemes each have advantages and disadvantages, one common factor is the need for highly efficient power amplification. As these communication devices become smaller and smaller, the functionality provided by these devices continues to increase. One major concern when developing these handheld communication devices power consumed and dissipated become smaller and smaller, the amount of power consumed and dissipated becomes more and more critical. Efficient power amplification decreases the amount of power consumed, thereby maximizing battery life of the device.
Another major concern in these wireless devices is the size of the circuitry. In order to minimize the hardware required it is desirable to integrate as much functionality as possible into fewer and fewer circuit modules. This enables the handheld device to be smaller and consume less power.
Another matter of concern is maintaining a highly efficient level of amplification while preventing the radio frequency signal that is supplied to the power amplifier from being coupled back into the circuitry that is used to bias the power amplifier. For the bias circuitry to provide the most consistent bias voltage and current, it is important that the RF input signal not modulate the bias circuitry. When the RF input signal migrates into the bias circuitry, fluctuations are caused in the bias voltage. These fluctuations cause performance degradation and power output variations in the power amplifier.
Therefore, there is a need in the industry for a bias circuit for a power amplifier where the bias circuit is resistant or desensitized from any RF energy coupled back into the bias circuit.